The present invention relates to an image forming apparatus employing an electrophotographic method, such as a copying machine, a printer and a facsimile machine, and to an image forming system having functions thereof.
In the aforesaid image forming apparatus and the aforesaid image forming system, there has been a problem wherein density of an image is changed by environmental changes in the course of printing and by fluctuations of apparatus characteristics, resulting in scattering of image qualities among a plurality of images printed under the same conditions.
For the aforesaid problem, in the case of a calibrating method disclosed in Japanese Patent Publication No. 4284520, when there are environmental changes in the course of printing or fluctuations of apparatus characteristics, a test image is formed on a sheet, then, the test image is measured by a color measuring sensor, and color proofreading processing is conducted based on the measured value, each time of the environmental changes and the fluctuations of the apparatus characteristics.
Incidentally, when conducting the color proofreading processing based on the measured value by the color measuring sensor, conversion data that show relationship between the measured value of the color measuring sensor and the image density are needed. These conversion data are changed in accordance with a screen that is selected according to a type of a sheet on which an image is formed and to an attribute of the image.
However, in the conventional color proofreading processing, the same conversion data are used even when the type of the sheet and a screen of the image are changed. Therefore, it is not possible to conduct appropriate density adjustment processing in accordance with a type of a sheet and with a screen of an image, because appropriate conversion data are not selected according to the sheet type and the screen for the image.